Every day thousands of tons of petroleum-based plastic waste accumulate in the environment, resulting in growing non-biodegradable landfills and escalating waste disposal costs. A solution to this problem is to use biodegradable alternatives to plastics, one such alternative being polyhydroxyalkanoates (PHA), a family of high-performance, highly marketable biodegradable polymers possessing excellent physical properties suitable for a wide range of industrial applications.
PHA is a macromolecule produced by many bacteria. It is a polyester molecule composed of hydroxyl fatty acid monomer subunits. It is UV-stable, resistant to extreme temperatures, and resistant to permeation by water. Unlike petroleum-based plastics that can take centuries to degrade, PHA-based plastics are completely biodegradable when placed in decomposition environments such as landfills or composting sites. Furthermore, if accidentally placed in the earth's oceans, PHA-based plastics degrade quickly without any harmful effects on sea life or the greater ocean environment from chemical residues or other pollutants. In addition to these properties, PHA is also biocompatible, gradually breaking down harmlessly without inducing an inflammatory response in the body.
PHA production is based on renewable resources as opposed to diminishing fossil fuel stockpiles. PHA can be commercially produced in bacterial fermentation processes using substrates to drive microorganism growth and PHA synthesis. These substrates can be agricultural products, e.g., sugar and fatty acids.
The most common form of PHA produced is a blend of polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV), which has properties very similar to polypropylene currently found in many containers, housewares, and automotive parts. Because of its biocompatibility, PHA-based plastics can also be used in biological applications, such as medical sutures, tissue repair devices, or for other biomedical uses.
The favorable properties of PHA provide incentives to develop efficient ways of producing PHA using biological systems. Despite the advantages of using PHA plastics, the high price of PHA compared to the low price of petrochemical-based plastics has significantly limited its widespread use. Several factors are critical for economic production of PHA: substrate costs, fermentation time, and efficiency of downstream processing. The current production processes, dependent on genetically modified organisms (GMOs), have numerous limitations, such as requiring strict environmental controls, sterile operating conditions, and relatively expensive feedstocks.
Thus, there exists a need to develop cost-effective and efficient biological systems to produce PHA, in particular, microorganisms capable of producing high yields of PHA from cheap, readily available, and renewable feedstocks such as organic wastewater.